More weapons , More variation in common infected , more maps , and a god.damn matchmaking system for versus typed gamemodes.I'm fine with the SI , but I would also be fine with it if they added maybe 1 or 2 new SI.

I would like a new playable infected aim down sights with the gun and for a Mutation called"Grief" two survivior teams 1 Infected team all trying to stop each other from winning so its kinda like Survivors vs Survivors vs Infected

for the l4d1 and l4d2 survivors to meet again and the l4d1 survivors stick with the l4d2 survivors

Way to think originally. The L4D suriviors are in the keys, this fact is canon, and the L4D2 survivors are supposedly in either New Orleans or a Carrier detainment center nearby. If L4D3 is coming and will be set in a new and different location as most people want, any more interaction between different generations of Survivors would be blatant catering to the fans at this point.

Well, i think that l4d2 already has too many ideas, if not all of them, but maybe new special infected, or explosive weapons (e.g. grenade launcher or RPG), lethals like grenade and something like a booby trap to avoid butt-sex from hordes coming from behind.